contrast

Splicing (genetics)

...ed codons) and introns (interrupting codons). In contrast to prokaryotes , which do not usually have introns, eukaryotes initially create a primary mRNA transcript called pre-mRNA that is composed of both introns and exons (see transcription ). Pre-mRNA has to be spliced before it can be translated i...

RNA

...are genes that encode functional RNA molecules; in contrast to mRNA, these RNA do not code for proteins. The best-known examples of RNA genes are transfer RNA ( tRNA ) and ribosomal RNA ( rRNA ). Both forms participate in the process of translation , but many others exist. RNA forms the genetic materia...

Red Queen

...chard Dawkins ) can be achieved by considering the contrast between two adaptations of the polar bear . This animal has a coat of hair which is thick to help the bear survive the cold of the arctic and white in order that the bear can stalk seals for food. For the first case the selection pressure is lik...

Punctuated equilibrium

...ressed the gradual nature of evolution, to clearly contrast it with the then-popular catastophism, it is often incorrectly assumed that he insisted that the rate of change be constant or nearly so. Punctuation appears also to be compatible with the independent proposals of the theory of evolution by natural ...

Prokaryote

... meaning nut, referring to the nucleus. This is in contrast to eukaryotes , organisms that have cell nuclei and may be variously unicellular or multicellular. The difference between the structure of prokaryotes and eukaryotes is so great that it is considered to be the most important distinction among group...

Peripheral membrane protein

... peripheral membrane proteins. These proteins, in contrast to integral membrane proteins, tend to collect in the water-soluble fraction during protein purification . An exception to this rule is that cells may attach an "anchor" moiety, such as the fatty-acid anchor of lipid anchored proteins , which mak...

Origin of life

... building blocks from simple gaseous compounds. In contrast to the classical Miller experiments, which depend on external sources of energy (e. g. simulated lightning or UV irradiation), "Wchtershuser systems" come with a built-in source of energy, sulfides of iron and other minerals (e. g. pyrite). The e...

Magnetic resonance imaging

...most medical examinations. Often, a paramagnetic contrast agent, a gadolinium compound, is administered, a...m each other as separate), MRI provides far better contrast resolution (the ability to distinguish the differences between two arbitrarily similar but not iden...

Microscope

... techniques are usually necessary to increase the contrast in the image to useful levels (see contrast methods ). Typically, on a standard compound optical microscope, there are three objective lenses: ...

Lung

...same direction - posterior to anterior. This is in contrast to the mammalian system, in which the direction of airflow in the lung is tidal, reversing between inhalation and exhalation. By utilizing a unidirectional flow of air, avian lungs are able to extract a greater concentration of oxygen from inhaled ai...

Human

...ences perceived as pleasant, like love or joy , contrast with those perceived as unpleasant, like hate , envy , or jealousy . In Penses , Blaise Pascal wrote of the emotions: Weariness — Nothing is so insufferable to man as to be completely at rest, without passions, without business, witho...

Gene therapy

...genic (most people carry this harmless virus). In contrast to adenoviruses, most people treated with AAV will not build an immune response to remove the virus and the cells that have been successfully treated with it. Several trials with AAV are on-going or in preparation, mainly trying to treat muscle and e...

Gel electrophoresis

...t looks and feels like clear jello. Acrylamide, in contrast to polyacrylamide, is a neurotoxin and needs to be handled using Good Laboratory Practices (GLP) to avoid poisoning. The second part, " electrophoresis ", refers to the electromotive force (EMF) that is used to push or pull the molecules throu...

Facilitated diffusion

...hape, to wait for more molecules to transport. In contrast to active transport , facilitated diffusion does not require energy and carries molecules or ions down a concentration gradient....

Bacterium

...prokaryotes , because bacteria are prokaryotes, in contrast to organisms with more complex cells, called eukaryotes . The term "bacteria" has variously applied to all prokaryotes or to a major group of them, depending on ideas about their relationships. Bacteria are the most abundant of all organisms. The...

Endergonic reaction

... which ΔG > 0 in Gibbs free energy , in contrast to an exothermic reaction , which uses ΔH as in enthalpy . See also: exergonic reaction...

Gel electrophoresis

...t looks and feels like clear jello. Acrylamide, in contrast to polyacrylamide, is a neurotoxin and needs to be handled using Good Laboratory Practices (GLP) to avoid poisoning. The second part, " electrophoresis ", refers to the electromotive force (EMF) that is used to push or pull the molecules throu...

Cytoplasm

...membrane , in which organelles are suspended. In contrast to the protoplasm , the cytoplasm does not include the cell nucleus , the interior of which is made up of nucleoplasm . Components of the cytoplasm The aqueous component of the cytoplasm (making up 80 percent of it) is composed of ions and...

Culture

...ial critics, from the 18th century on, accept this contrast between cultured and uncultured, but emphasize tha...ltured in a different way. Thus, social observers contrast the "high" culture of elites to "popular" or pop culture , meaning goods and activities produce...

Computed axial tomography

...s a guide for interventional procedures. Sometimes contrast materials such as intravenous iodinated contrast is used. This is useful to highlight structures such as blood vessels that otherwise would be diffic...

Carnivore

...lso cannibalism insectivore Compare and contrast herbivore omnivore...

Bone

...ed at random, and as a result has low strength. In contrast lamellar bone has parallel fibres and is much stronger. Woven bone is often replaced by lamellar bone as growth continues. Long bones are tubular in structure (e.g. the tibia ). The central shaft of a long bone is called the diaphysis , and has...

Biochemistry

...organic compounds can be created artificially, in contrast to the common belief of the time that organic compounds could only be made by living organisms. It is generally accepted that the term biochemistry was coined in 1903 by Carl Neuber, a German chemist . Since then, biochemistry has advanced, espe...

Bacterium

...prokaryotes , because bacteria are prokaryotes, in contrast to organisms with more complex cells, called eukaryotes . The term "bacteria" has variously applied to all prokaryotes or to a major group of them, depending on ideas about their relationships. Bacteria are the most abundant of all organisms. The...

Apoptosis

... unwanted cell in a multicellular organism . In contrast to necrosis , which is a form of cell death that results from acute tissue injury, apoptosis is carried out in an ordered process that generally confers advantages during an organism's life cycle. For example, the differentiation of human fingers...

Anaphase

...spindle to around twice its metaphase length; in contrast yeast and certain protozoa use anaphase B as the main means of chromosome separation and can extend the spindle to up to 15 times its metaphase length in the process. See also gamete cytokinesis prophase prometaphase metaphase ...

Adaptive radiation

.... Environmental change. A species that can, in contrast to the other species in the ecosystem, successfully survive in a radically changed environment will probably branch into new species that cover the new ecological niches created by the environmental change. An example of adaptive radiation as the res...